I believe I understand the feeling you are describing. I've often had this experience with changes of a similar magnitude.

Incidentally, I can see the risk of falling into the subjectivist trap with these posts but this is the basis for this post for me. It frustrated me that I couldn't put it into numbers (or explainable phenomena or whatever).

I do suspect this....that some changes in frequency response will mask or enhance parts of the spectrum. Most often I think, when you remove an offending region it lets others stand out. On the other hand, I know that I've added, oh let's say midrange, and found the bass now stands out as it is better supported. It can sound deceptively as if you've changed a woofer when you only touched a tweeter.

Taking this to another level...phase changes can cause some interesting frequency response effects. On axis can change (say, reduce...), whilst the in room power reponse can be increasing in level. This, by the way, I suspect (and pretty much blame) for the subjective difference with my earlier measurement procedures between what I saw and what I heard.

Last edited by AllenB; 24th August 2011 at 10:23 AM.
Reason: Edit: got caught in the diyaudio nightly maintenance with this post.